The present invention relates to a conduction breaking device that breaks conduction between two devices constituting an electric circuit by cutting a conductive body extending between the devices.
Some electric circuits are provided with a conduction breaking device for breaking conduction between devices by being activated when a malfunction occurs in a device in the electric circuit or in a system on which the electric circuit is mounted. As one form of such conduction breaking devices, Japanese Laid-Open Patent Publication No. 2014-49300 discloses a conduction breaking device C shown in FIGS. 16A and 16B, which includes a conductive body 80, a gas generator (not shown), a fixed blade 84, and a cutting member 85.
The conductive body 80 includes an elongated plate-shaped cuttable portion 81 and is arranged between devices that constitute an electric circuit. The gas generator is arranged on one side of the cuttable portion 81 with respect to the thickness direction (on the lower side as viewed in FIG. 16A). The fixed blade 84 is arranged on the opposite side of the cuttable portion 81 from the gas generator with respect to the thickness direction. The cutting member 85 includes a movable blade 86 and is arranged between the cuttable portion 81 and the gas generator.
The cutting member 85 receives the pressure of the gas generated by the gas generator and is moved toward the cuttable portion 81. As the cutting member 85 is moved, the cuttable portion 81 receives shearing force generated by the fixed blade 84 and the movable blade 86. The shearing force cuts the cuttable portion 81 along the width. When the cuttable portion 81 is cut over the entire width, a pair of cut edges 82, 83 is formed in the cuttable portion 81. As shown in FIGS. 17A and 17B, the cut edges 82, 83 are separated from each other in the longitudinal direction and the thickness direction of the cuttable portion 81, so that the conduction between the devices is broken.
When the conductive body 80 in a current-carrying state is cut as described above, an arc may be generated due to the potential difference between a part of the cut edge 82 that is cut at the end (a cut end 82e) and a part of the cut edge 83 that is cut at the end (a cut end 83e). An arc refers to a phenomenon in which insulation of gas present between the cut ends 82e, 83e is broken and a current flows between the cut ends 82e, 83e. 
When an arc is generated, the cut ends 82e, 83e are electrically connected to each other. In this case, although being physically cut, the conductive body 80 may remain in a current-carrying state, in which conduction is not broken. Additionally, the arc may melt the conductive body 80 and its surrounding plastic members.
In this regard, the conduction breaking device C disclosed in Japanese Laid-Open Patent Publication No. 2014-49300 has an arc-extinguishing chamber 87. Surrounding walls that define the arc-extinguishing chamber 87 are made of a material having the electrical insulating property. The arc-extinguishing chamber 87 is arranged on the opposite side of the cuttable portion 81 from the gas generator with respect to the thickness direction of the cuttable portion 81 (on the upper side as viewed in FIG. 16A) and is adjacent to the fixed blade 84.
Thus, a part of the broken cuttable portion 81 that has the cut edge 82 is located close to the fixed blade 84, and a part that has the cut edge 83 is pushed into the arc-extinguishing chamber 87 by the movable blade 86. The cut edge 83 is moved away from the cut edge 82, and the arc generated between the cut ends 82e, 83e is attenuated in the arc-extinguishing chamber 87.
An arc has the property of flowing along the shortest one (shortest path RS) of the electric short circuit paths connecting the cut ends 82e, 83e. When the cut ends 82e, 83e are located at the central portion in the width direction of the cuttable portion 81, a path that extends in the longitudinal direction and the thickness direction of the cuttable portion 81 in the arc-extinguishing chamber 87 forms the shortest path RS. Thus, an arc flows along the shortest path RS in the arc-extinguishing chamber 87 and is properly attenuated in the arc-extinguishing chamber 87.
However, depending on the dimensional accuracy and the assembly accuracy of the components of the conduction breaking device C, the positions of the cut ends 82e, 83e in the width direction of the cuttable portion 81 vary. If the cut ends 82e, 83e are located at one of the edges in the width direction of the cuttable portion 81 as shown in FIG. 16B, a path through the outside of the arc-extinguishing chamber 87 forms the shortest path RS. Therefore, an arc flows along the shortest path RS through the outside of the arc-extinguishing chamber 87 as shown in FIGS. 16A, 16B and FIGS. 17A, 17B. In this case, the arc may not be properly attenuated.